The present invention relates to a device and method for antenna alignment, and more particularly to a method of antenna alignment which is useful inter alia for the backhaul connections in a cellular telephone network.
There are many methods used for antenna alignment and for an associated alignment mechanism. Some of them rely on geographical data, others rely on received signal level measurements and some incorporate motors in order to align the antenna. In most of the cases the antenna alignment solution is limited to the scope of one antenna to be aligned.
A relatively early example of automatic antenna alignment is illustrated by U.S. Pat. No. 5,551,058 assigned to Thomson Consumer Electronics Inc. Here a satellite receiver is aligned to a satellite. The receiver, which is for digitally encoded television signals, includes apparatus for aligning the receiving antenna to the satellite. The alignment apparatus is responsive to the number of errors contained in the digitally encoded television signals. Error correction is possible if the number of errors is below a threshold and not possible if the number of errors is above the threshold. The elevation of the antenna is set according to the location of the receiving site. Thereafter, the azimuth of the antenna is coarsely aligned by first rotating the antenna in small increments to locate a region in which error correction is possible. During this coarse alignment procedure, the tuner of the satellite receiver attempts to locate a tuning frequency at which demodulation and error correction is possible. If no appropriate frequency is found after a range of frequencies have been searched, the antenna is rotated by a small increment. Once error correction is found to be possible, a fine alignment procedure is initiated in which the antenna is rotated to locate boundaries of an azimuth are through which error correction is continuously possible. Thereafter, the antenna is set so that it is at least approximately midway between the two boundaries of the arc.
The satellite beam however is a broadcast beam and thus has a wide arc, which is intended to cover an entire region of television viewers. The automatic alignment based on error correction is not satisfactory when a narrow beam is being broadcast. Antenna alignment for narrow beam is known for beams below a certain frequency where the beam width is in fact not that narrow. Solutions based on GPS coordinates and on use of an optical gunsight are known. However the higher the frequency the narrower the pencil beam can be and existing methods of antenna alignment break down. At E-band frequencies, including frequencies of 71-76 GHz, which are of particular interest in the cellular backhaul field, there are no known automatic methods. Backhaul may be used for transmission of information between cellular base stations.